This invention relates to mechanical indicators, more particularly to mechanical gauges used on vehicles to indicate brake lining wear.
In vehicle braking mechanisms of the type using a cam positioned between two brake shoes and activated by a rotatable camshaft, it is common practice to accomplish movement of the cam by attaching to the cam a motor driven actuating lever. Because of the stroke limitations of the engine activating the lever rotating the brake cam a compensating device was built into the lever to make up for the brake lining wear taking place inside the brake drum compartment. These types of levers are known as slack adjusting levers, which can be manually or automatically adjusted. As the brake lining wears out inside the brake drum compartment a compensating adjustment is made on the slack adjusting lever outside the brake drum compartment. The method of compensating adjustment is done by rotating the brake camshaft inside the hub of the slack adjusting lever. The accumulated amount of rotational adjustments made inside the hub of the slack adjusting lever causing a differential between the cam and the lever becomes a source for accumulating brake lining wear data.
When brake linings wear out, compensating adjustments becomes essential in order to minimize the amount of travel the adjustable lever needs to travel in order to apply the brakes. The purpose of the wear indicator dial gauge is to disclose the amount of compensating adjustment that has taken place during each of the slack adjustments, this is done by comparing the calibration marks on the brake lining wear indicator gauge with the alignment mark 18 on original equipment slack adjusters or by virtue of a straight edge ruler forming an axial center line starting from the center of the clevis pin hole 20 on the slack adjusting lever to the machined centering hole on the splined end of the rotating camshaft axially mounted in the hub of the lever.
The standard procedure used by the industry for checking the amount of brake lining wear taking place inside a brake drum compartment is done by removing a brake drum, by removing an inspection cover at the rear of the brake drum compartment or by peeking through a specially positioned inspection hole in order to get a visual assessment of the amount of brake lining wear.
It has been proposed to make this brake lining wear information externally visible in the form of a register in order to assist the brake service mechanic and the operator of the vehicle in assessing the condition of brake linings inside a brake drum compartment without having to remove a wheel to get the same information.
By connecting the brake lining wear indicator to the axle of the brake camshaft every time the brake camshaft rotates inside the hub of the slack adjusting lever when brake adjustments are made to the brakes on a vehicle so simultaneously the brake lining wear indicator gauge rotates with the brake camshaft. The brake lining wear indicator gauge remains constantly fixed on the end of the brake camshaft as a visual register and an external reminder of the amount of adjustment travel that has taken place since the beginning of the brake adjusting cycle.
The proposed mechanisms for recording brake lining wear prior to this invention have not been without some difficulties and some modifications to the existing brake mechanisms. In the case of one prior device having two co-acting members namely a stator and a rotor also called an index and a co-acting dial plate, this system proved to be mechanically uneconomical because of having to adapt to the variation in size and styles of slack adjusting levers of the manual and automatic kind, difficulty was encountered with the attaching tabs of the co-acting parts to the brake mechanism.
Other problems encountered with prior dual component co-acting brake lining wear gauges was the indicator tabs protruding from the face of the dial, these few protruding tabs being exposed to the road hazards on gravel roads were continually getting bent giving the brake service mechanic and the vehicle operator a distorted reading of the brake lining wear.